As driving assistance control executed by a vehicle driving on a dirt road which is an unpaved road surface, vehicle downhill control such as DAC (Downhill Assistant Control) is known. In the vehicle downhill control, a brake actuator is actuated to prevent a vehicle body speed of the vehicle from exceeding a target speed (for example, 5 km/h) so as to adjust braking force to be applied to the vehicle.
Even though the vehicle downhill control is executed in a vehicle driving on a downhill slope, the driver of the vehicle may execute an accelerator operation. In this case, a target speed is designed to be determined depending on a vehicle body speed correlated with a maximum wheel speed of the wheel speeds of a plurality of wheels mounted on the vehicle (for example, see Patent Literature 1).